I would say a combination of:
- Good Gameplay - not too repetitive (Sierra's Quest series)
- Nice to fantastic graphics usage (Sierra)
- Original and catchy music (M.U.L.E., Elite)
- Multiplayer (M.U.L.E. - even if only in turn based)
- Multilevel (make it harder for the trained)
- for the more modern h/w: Networkability
I think if you don't copy the graphics, but design a 3D view, the boardgame "Colonists of Catan" would make a great multiplayer/online game. Only thing to really add: music/soundFX.
The PC Version of the Game only does Multiplayer through the network, but added characters and animated sequences.
Could easily be done on an AMIGA, too. :-D
